1. Field of the Invention
The present invention relates to a turbo-molecular pump that is used in vacuum apparatuses such as a semiconductor manufacturing apparatus and an analysis apparatus, in a pressure range from medium vacuum through ultra-high vacuum.
2. Description of the Related Art
Conventionally, in a dry etching process, a CVD process, or the like in semiconductor manufacturing processes, processing is performed while supplying a large amount of gas in order to perform the processes at high speed. Generally, a turbo-molecular pump that is provided with a turbine blade section and a screw groove pump section is used as a vacuum pump that evacuates a process chamber in a semiconductor manufacturing apparatus that performs these processes. When the turbo-molecular pump is used in these processes, a reaction product may be accumulated inside the pump depending on the type of process gas. In particular, the reaction product is likely to be accumulated on the screw groove pump section having a relatively high pressure because of the relationship between the pressure and the sublimation temperature in the reaction product.
Thus, in a turbo-molecular pump described in JP 2003-278692 A, a heater and a water-cooled pipe are disposed on a pump base, and energization of the heater and supply of cooling water are controlled to thereby monitor the temperature of a gas flow passage in a screw stator or the like so as not to drop to a preset temperature or less. This prevents accumulation of a reaction product.
A turbo-molecular pump discharges gas by rotating a rotor at high speed. Generally, an aluminum alloy is used in the rotor. A temperature at which a creep phenomenon occurs in aluminum is lower than that in other metals. Thus, in a turbo-molecular pump in which a rotor rotates at high speed, it is necessary to suppress the temperature of the rotor lower than a creep temperature range.
On the other hand, when a large amount of gas is discharged in the turbo-molecular pump, heat is generated in response to the gas discharge, which results in an increase in the temperature of the rotor. Heat release from the rotor is mainly performed by radiation from rotor blades to stationary blades or heat transfer through gas. However, as described above, in the configuration which controls energization of the heater and supply of cooling water to maintain the temperature of the screw stator or the like higher than the preset temperature, the temperature of the stationary blades during gas discharge becomes higher than the temperature of the screw stator. Accordingly, heat release from the rotor blades to the stationary blades is not sufficiently performed, and the temperature of the rotor is thus likely to increase. Therefore, disadvantageously, it is not possible to increase the exhaust flow rate.